Generally described, gas turbine buckets may have a largely airfoil shaped body portion. The buckets may be connected at the inner end to a root portion and connected at the outer end to a tip portion. The buckets also may incorporate a shroud about the tip portion. The shroud may extend from the tip portion so as to prevent or reduce hot gas leakage past the tip. The use of the shroud also may reduce overall bucket vibrations.
The tip shroud and the bucket as a whole may be subject to creep damage due to a combination of high temperatures and centrifugally induced bending stresses. One method of cooling the bucket as a whole is to use a number of cooling holes extending therethrough. The cooling holes may transport cooling air through the bucket and form a thermal barrier between the bucket and the tip shroud and the flow of hot gases.
Although cooling the bucket may reduce creep damage, the use of the air flow to cool the bucket may reduce the efficiency of the turbine engine as a whole due to the fact that this cooling air is not passing through the turbine section. Further, the effectiveness of the cooling air diminishes as the air moves from the bottom to the top of the bucket. This diminished effectiveness may lead to higher temperatures towards the exit of the bucket about the tip shroud due to less cooling.
There is thus a desire for bucket cooling systems and methods that provide adequate cooling to prevent creep and increase bucket life while improving overall turbine performance and efficiency.